Steel cords (in what follows ‘cord’ will be used as synonym for ‘rope’ or ‘cable’), used for example in timing belts, elevator belts, etc., normally work in tension and are subjected to bending under loads. The characteristics of particular importance required for such cables are strength, excellent fatigue properties, uniform permanent elongation and improved adhesion.
Such steel cords are sometimes interiorly provided with an elastomer filler, because it is well known in the state of the art that elastomer filled steel cord have properties superior to those of equal size bare steel cord. These improved properties are derived from the separation of the core strand from the outer strands and the outer strands from each other by the elastomer filler. Suitable thermoplastics include polypropylene, polyurethane, polyethylene, poly-amide, poly-tetrafluorethylene or polyvinylchloride. Also used are elastomers such as butyl or nitrile rubber. The elastomer filler reduces or eliminates the core to strand and strand to strand contact and abrasion when the steel cord is in service.
A method for filling a steel cord is described in for example EP 0530445, where poly-butadiene is extruded on the filaments or strands of a steel cord and cured. Such a process is not applicable when the necessary feed rate of the components drops below 5 to 10 ml/min. For example steel cords comprising filaments below about 0.30 mm can not longer be coated by means of such a system. Furthermore, extrusion is an expensive technique.
Another method is described in US patent application 2002/0189227, wherein a cable is produced by depositing the polymer material over the core and/or strands with an injection head a certain distance upstream of the cabling point and wherein in the injection head a pre-polymer and a polymerization accelerator are mixed and immediately deposited. However this process is suffering from uncontrolled curing, since upon depositing, the polymer material is already curing.
Another method of filling a steel cord is described in WO2007/020156, wherein the steel cord is dipped in an aqueous microemulsion containing polymers, followed by heating. A disadvantage of this method is that possibly remaining water may cause corrosion.